Wegovy vs Zepbound — 7 proven differences you should know.

Wegovy vs Zepbound is one of the most searched comparisons in weight management — and the confusion is understandable. Both are once-weekly injections, both treat obesity, and the names sound similar enough to blur together. But they are genuinely different medications: Wegovy contains semaglutide, the same active ingredient as Ozempic. Zepbound contains tirzepatide, the same active ingredient as Mounjaro. In May 2025, the first direct head-to-head trial — SURMOUNT-5 — settled the question of which produces more weight loss, and the result was decisive. This guide covers exactly what the difference is, what the data shows, and which medication is right for which patient.

All data in this guide is drawn from the SURMOUNT-5 Phase 3b trial published by Eli Lilly, alongside the NHS obesity treatment guidance. Note: Zepbound is the US brand name for tirzepatide; in the UK the equivalent medication is sold as Mounjaro.

Is there a real difference between Wegovy and Zepbound?

Yes — a substantial one. Wegovy vs Zepbound is not a case of two brand names for the same drug, the way Ozempic and Wegovy are both semaglutide. Wegovy and Zepbound are two entirely different molecules made by two different pharmaceutical companies, working through different — though related — mechanisms. Wegovy is manufactured by Novo Nordisk. Zepbound is manufactured by Eli Lilly. The active ingredients, semaglutide and tirzepatide, are chemically distinct compounds.

Mechanism — how Wegovy and Zepbound differ

The core distinction in the Wegovy vs Zepbound comparison is the number of hormonal pathways each medication activates:

• Wegovy (semaglutide): a single-hormone GLP-1 receptor agonist. It mimics glucagon-like peptide-1, slowing gastric emptying, signalling fullness to the brain, and reducing appetite
• Zepbound (tirzepatide): a dual-hormone agonist activating both GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors simultaneously. GIP enhances insulin secretion and improves fat metabolism, working synergistically with GLP-1 to amplify the appetite-suppressing and metabolic effects beyond what either hormone achieves alone

This single-versus-dual mechanism difference is the reason every head-to-head trial between semaglutide and tirzepatide-based medications has shown tirzepatide producing greater weight loss — a pattern confirmed again in Wegovy vs Zepbound specifically.

SURMOUNT-5 — the head-to-head result

SURMOUNT-5 was the first direct clinical comparison between the two medications — a Phase 3b, open-label, randomised trial sponsored by Eli Lilly. It enrolled 751 participants with obesity or overweight plus at least one weight-related condition (hypertension, dyslipidaemia, obstructive sleep apnoea, or cardiovascular disease), none of whom had diabetes. Participants received either the maximum tolerated dose of Zepbound (10mg or 15mg) or Wegovy (1.7mg or 2.4mg) for 72 weeks.

The result, published in the New England Journal of Medicine in May 2025: Zepbound produced an average of 20.2% body weight reduction, compared to 13.7% for Wegovy — a 47% greater relative weight loss. In absolute terms, participants on Zepbound lost an average of 50 pounds, compared to approximately 33 pounds for those on Wegovy. Zepbound beat Wegovy on the primary endpoint and all five key secondary endpoints, including the proportion of patients reaching 10%, 15%, 20%, and 25% weight loss thresholds.

Wegovy vs Zepbound side by side

Different approvals — what each does beyond weight loss

Beyond raw weight loss numbers, Wegovy vs Zepbound diverges in what each medication is specifically approved to treat:

• Wegovy is approved to reduce the risk of serious cardiovascular events — heart attack and stroke — in adults with established cardiovascular disease and either obesity or overweight, based on the SELECT trial. It is also approved to help treat MASH (metabolic dysfunction-associated steatohepatitis), a serious form of fatty liver disease
• Zepbound is approved for treating moderate-to-severe obstructive sleep apnoea in adults with obesity — an approval Wegovy does not currently hold

This means the right choice in the Wegovy vs Zepbound decision is not always simply “whichever produces more weight loss” — a patient with established cardiovascular disease or MASH may have additional clinical reasons to consider Wegovy specifically, regardless of the weight loss differential.

Side effects compared

Both medications in the Wegovy vs Zepbound comparison share a broadly similar gastrointestinal side effect profile — nausea, vomiting, diarrhoea, and constipation, most pronounced during dose escalation. Both also carry a boxed warning regarding thyroid C-cell tumours observed in animal studies, with tirzepatide and semaglutide both contraindicated in patients with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2.

Some patients report that Zepbound’s dual mechanism produces somewhat more pronounced early GI side effects during escalation, reflecting its more potent metabolic action — though individual tolerability varies considerably and is not reliably predictable from the mechanism alone.

The UK equivalent — Zepbound is Mounjaro

The most important practical point for UK readers researching Wegovy vs Zepbound: Zepbound is not available in the UK under that name. Zepbound and Mounjaro are the identical medication — tirzepatide, made by Eli Lilly — sold under different brand names in different markets and for different primary indications. Mounjaro is MHRA licensed and widely available in the UK via private prescription and from Mymetabolism. Wegovy is also MHRA licensed and available in the UK. So the practical UK comparison is Wegovy vs Mounjaro — see our complete Mounjaro vs Ozempic guide for the equivalent UK-branded breakdown.

Which one is right for you?

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